Friday, July 30, 2010

A week ago, on Friday, July 23, 2010, a severe thunderstorm hit the town of Vivian, South Dakota. That storm ended up not only producing hail, but the largest hailstone to ever be recorded as long as records have been kept.

The hailstone, as seen on the left, was an amazing 8" in diameter and weighed 1.9 lbs.

The previous record for the largest hailstone recorded occured back in 2003 in Aurora, Nebraska, when a hailstone measured 7" in diameter.

To give you some perspective on how big that hailstone was, here is a chart comparing hail size to a real object.

The bottom line is in order for a thunderstorm to produce large hail, you need a very unstable atmosphere and very cold air in the mid to upper levels of the atmosphere. As air rises, it cools and condenses into water droplets. If the vertical motion is strong enough, some of these droplets can freeze and combine with other water molecules to form hail.

Thursday, July 29, 2010

With plenty of tropical moisture and slightly above normal rainfall for the months of June and July, temperatures were not as hot as they could have been.

We will finally get a taste of what real summers feel like in East Texas by this weekend as a big dome of high pressure settles in over the Southern Plain states.

Underneath these areas of high pressure, you get a lot of sinking air. When you compress air, it heats up.

It's often like airing up a bicycle tire. After you compress the air in your tire and take out the pump, the tire feels hot. The same process is what happens when areas of high pressure set up overhead in the summer time.

While the heat will be present, the rain showers will be virtually non-existent. That sinking air will limit the cloud development and keep the showers from forming during the afternoon hours.

We will see upper 90's on Friday, followed by triple digit heat by the time we head towards Sunday and Monday of next week.

Friday, July 23, 2010

Bonnie has been downgraded from a tropical storm to a tropical depression this evening. The biggest factor for this weakening system has been very strong winds in the upper levels of the atmosphere.

These strong winds are shearing apart the cloud tops, preventing Bonnie from getting organized and strengthening.

This is certainly good news for residents along the Gulf coast, who now just will only have to deal with rain and nothing more.

The image above shows the latest forecast track from the National Hurricane Center. Notice how thin the cone is in the track. That narrow range in the cone represents high confidence in the forecast track, something we like to see.

It appears that Bonnie will make its second landfall late Saturday evening or early Sunday morning between Mobile, AL and Morgan City, LA.

By being west of the low pressure center, that will put us on the back side of the system, giving us some tropical rain showers.

Here is a timeline of what we can expect from this system here in Deep East Texas

Saturday: Hot and humid with an isolated shower late.

Sunday: Increasing clouds with rain becoming more numerous, especially during the afternoon hours.

Thursday, July 22, 2010

At this time the storm is very disorganized and is encountering some wind shear on the west side of the system. As you can see from the satellite image, most of the showers and storms are displaced along the northeast side of the low pressure center.

Bonnie will continue on its westward track and has its sights set on the Gulf of Mexico.

This is not good news for the horizon oil spill sight, which will be impacted by the storm, regardless of whether or not Bonnie moves directly overhead. As of late this afternoon, the U.S. government ordered ships to evacuate the oil spill, as heavy rain and gusty winds are expected to arrive by Friday evening.

The big question everyone has is 'where will Bonnie go?'

According the the official forecast track from the National Hurricane Center, Bonnie looks to be a threat along the Gulf coast states. She could make landfall anywhere from the mouth of the Mississippi to as far west as the upper Texas coast.

Notice that we are in the forecast cone of uncertainty. Keep in mind that this forecast cone will shift over the next few days as computer models try to get a better handle on the storm and the steering currents coming into play.

Nevertheless, you should be monitoring this storm closely as we head into the weekend. Even if it does not strengthen into a hurricane, we could still feel some of Bonnie's effects in the form of heavy rain and gusty winds.

Make sure you check out our Hurricane Center to get the latest updates 24/7 on the storm. We will continue to provide extensive coverage on KTRE-TV as well, keeping you informed with the latest information.

Tuesday, July 20, 2010

After a quiet couple of weeks in the tropics, things might be showing signs of heating up once again.

The latest tropical wave we are monitoring is producing heavy rain and gusty winds over Hispaniola, and Puerto Rico.

This flare up of showers and storms, as seen on the satellite image, is a sign that this wave is beginning to get better organized.

Even though it is not yet a named storm, that may change in the next couple of days as environmental conditions are favorable for development.

Hurricane Reconnaissance is scheduled to investigate this system on Wednesday. If they find a low level circulation at the surface, it could become a tropical depression by as early as tomorrow afternoon.

The one thing that may hamper this system is the fact it will be interacting with all the islands in the Greater Antilles. That could keep the storm disorganized, and ultimately, keep it from strengthening.

Make sure you keep it tuned to KTRE-TV and ktre.com. If this tropical wave strengthens into a tropical storm or hurricane, it will be given the name Bonnie.

Monday, July 12, 2010

After getting the month of July off to a cloudy and wet start, we will be settling back into reality this week.

By reality, I mean temperatures getting up into the upper 90's with heat index values in the 105-108° range.

Our heat will be returning in large part because of a ridge of high pressure that will be building across the Southern Plain states by mid-week.

As I've said several times, when you get high pressure in the mid-levels in the atmosphere during the summer months, that means hot and dry weather will prevail.

This high pressure ridge means the air temperatures aloft are very warm. This warm air prevents the clouds from building into afternoon rain showers. It puts a "lid" or "cap" on the atmosphere and keeps those cooling, afternoon rain showers from forming.

As the air sinks, it also heats up. You can think of this sinking air like airing up a bicycle tire. When you add air to the tire, you are compressing the air. As a result, the air heats up. That's why the tire is hot when you get done airing it up.

The same scenario plays out in the atmosphere when you get strong high pressure aloft.

In the meantime, plan on turning your sprinkler systems back on later this week, because your yards will be thirsting for some water.

After all, this ridge will steer any rainmakers well away from us over the next 5 to 7 days.

Wednesday, July 7, 2010

For the second week in a row, we have seen more clouds and less sun. We've also seen tropical downpours move through East Texas, dumping heavy amounts of rain.

Last week it was due to Alex, and all the moisture wrapping around that broad hurricane.

This week, we have the same song, just a different verse.

The tropical rain showers we have experienced over the past couple of days has come from a tropical low over Louisiana and an upper low over the lower Texas coast.

There is also a tropical wave that could develop into a depression or tropical storm by Thursday. That area of low pressure is shown in the image above, approaching northern Mexico and South Texas.

Regardless if that wave develops or not, we will still see plenty of moisture thrown in our direction, which will provide us with another round of heavy downpours.

With the above normal rainfall in the past week, we have been able to put a dent in our rainfall deficit. Just a week and a half ago, we had a deficit of -8.75". That deficit has been trimmed to -4.78", nearly erasing half of it.

Friday, July 2, 2010

Hurricane Alex made landfall on Wednesday, June 30, 2010, near Soto La Marina, Mexico, or about 110 miles south of Brownsville, TX.

It made landfall as a category 2 hurricane with winds of 105 mph.

While Alex was not a major hurricane, it is historic in a couple of perspectives.

Alex became the first June hurricane in the Gulf of Mexico since Hurricane Allison hit Florida 15 years ago, in 1995. We typically don't see hurricanes in the Gulf, this early in the season. So the fact we had a category 2 hurricane was unprecedented.

It was also the second strongest June hurricane since Alma, all the way back in 1966.

The most remarkable stat, however, was the pressure of Hurricane Alex. As it neared landfall it had a pressure of 947 mb. That pressure is typically seen when hurricanes are at a strong category 3 or weak category 4 status.

If you compare Alex to Hurricane Audrey, a category 3 hurricane that made landfall in Sabine Pass in 1957, it is almost identical. Audrey's pressure was 945 mb and had winds of 130 mph.

Alex had nearly the same pressure, but winds of only 105 mph.

So why the discrepancy in wind speeds if pressures were nearly the same? As I like to say, all hurricanes are different and take on their own characteristics.

Since Alex was such a broad storm, its winds were spread out over a large area. We saw the same thing a couple of years ago when Hurricane Ike made landfall as a strong category 2 storm.